The present invention relates to scintillators and related devices and methods. More specifically, the present invention relates to quantum dot scintillators for use, for example, in radiation detection, including gamma-ray spectroscopy, and X-ray imaging and neutron detection.
The emergence of new and exciting applications, such as those in high-energy nuclear physics and/or X-ray imaging, have demanded detector performance requirements that present the need for novel scintillators with exceptional properties. For example, synchrotron facilities have opened and continue to open avenues of research unthinkable a few years ago; in particular in the area of studying biological and other important materials. The availability of small angle X-ray scattering (SAXS) instruments on third generation synchrotron X-ray sources, with their high intensity and high degree of collimation, has been important for static and time-resolved studies of various non-crystalline biological systems. Other notable applications include static and time-resolved scattering from macromolecules in solution and phase transitions in model membrane systems. However, collecting X-ray data from such partially ordered and disordered systems presents formidable technical challenges. The scattering from those systems is intrinsically weak, and the time scales of interest may be at the millisecond and sub-millisecond level, challenging the ability of existing detectors to capture accurate and detailed data. Thus, while various SAXS instruments at third generation sources can deliver the required flux levels at the sample with exceptional beam quality, the availability of suitable detectors is still a limiting factor.
At present, the most practical design for synchrotron X-ray imaging detectors is based on a CCD optical detector coupled to a scintillating phosphor converter screen, although these detectors are beset with difficulties such as limited imaging area and slow readout speed. In addition, the performance of CCD/CMOS-based high frame rate detectors is limited by the characteristics of the phosphor screen used to convert the incident X-ray flux to visible light. High frame rate applications are inherently light starved, and no current phosphor can provide high enough conversion efficiency to detect low energy X-rays above the noise (dominated by the read noise in high frame rate systems). Low light-conversion efficiency also limits the signal-to-noise ratio (SNR) in measuring weakly diffracted peaks and intrinsically weak scattering from partially ordered and disordered systems, especially when data is acquired on the millisecond or sub-millisecond time scale using integrating detectors. This places constraints on designing detectors with the required active areas, as excessive light loss in coupling large-area screens to the limited-area CCD/CMOS sensors further degrades the SNR.
Furthermore, scintillation spectrometers are now routinely used in medical imaging, diffraction, homeland defense, nuclear waste cleanup, nuclear treaty verification and safeguards, and geological explorations, all of which need scintillators with improved performance, and further emphasize the need for economic, large detectors with, e.g., excellent X-ray/γ-ray response. New inorganic scintillators including rare earth halides such as LaBr3 and CeBr3, their elpasolites, and alkaline earth iodides (such as CaI2 and SrI2) doped with europium, have recently emerged as very promising scintillators for gamma-ray spectroscopy. Many of these materials provide energy resolutions that are a factor of two better than that of NaI:Tl detectors currently used. However, crystal growth of many of the new compositions (e.g., LaBr3 and CeBr3) is very challenging due to their significant anisotropy, leading to crystal cracking and reduced crystal yields, making them very expensive.
Existing scintillator materials and commercial radiation detectors do not meet the current needs for existing techniques for radiation detection of, e.g., ionizing radiation and X-ray imaging. Thus, a need exists for improved scintillator compositions suitable for use in various radiation detection applications.